Explore the vast range of titles available.

R744 is the most competitive and ideal natural refrigerant when flammability and toxicity are strictly limited. However, there are still some problems when it is applied to a heating system. For example, the discharge pressure of the system exceeds 10 MPa, it increases the cost of the system, and the cycle efficiency is also low. To solve these problems, this paper proposes to replace R744 by mixing R744 and ethane at a ratio of (77.6/22.4) to form an azeotropic refrigerant. At present, there is little research on R744 azeotropic refrigerant. Therefore, this paper first establishes the CFD model and compiles the UDF program to focus on flow boiling heat transfer characteristics, and then, it analyzes the performance of R744 and its azeotropic refrigerant in a low-temperature heating system. The results show that the heat transfer coefficient of R744 and its azeotropic refrigerant decreases with an increase in mass flux and increases with an increase in heat flux and saturation temperature; the heat transfer coefficient of azeotropic refrigerant is greater than R744; and there is no dryness under the same conditions. Under a given operating condition, there is a critical point that makes the performance of azeotropic refrigerant better than R744, and this critical point is related to the outlet temperature of a gas cooler, and the system discharge temperature of azeotropic refrigerant is significantly lower than that of R744. In conclusion, azeotropic refrigerant has certain advantages in heat transfer and system performance compared with R744, which will also play an important role in promoting the replacement of refrigerant in the future.

As global environmental consciousness continues to expand, the issue of refrigerant alternatives has increasingly become a focal point for scholarly attention. Using CiteSpace visualization technology, a comprehensive and innovative research framework for refrigerant alternatives has been developed. This framework systematically organizes and analyzes not only the volume of publications related to refrigerant alternatives but also the collaborative relationships among authors and research institutions. By employing keyword co-occurrence maps, clustering diagrams, and timeline charts, an in-depth analysis of the academic literature on refrigerant alternatives has been performed, elucidating the core research themes, evolutionary trajectories, and emerging trends in this field. Research indicates an exponential increase in the number of studies on refrigerant alternatives; however, there is insufficient collaboration and communication among researchers and institutions. Key research hotspots in this field encompass the organic Rankine cycle, vapor-liquid equilibria, pressure drop characteristics, vapor compression refrigeration systems, exergy analysis, alternative refrigerants, and performance evaluation of carbon dioxide systems. In future research, the performance of various low GWP refrigerants in refrigeration cycle systems will continue to be a focal point. To address diverse application requirements, developing blended refrigerants represents a pragmatic technical approach. From a sustainability standpoint, natural refrigerants are anticipated to emerge as the ultimate alternative, with the technical challenges associated with their application constituting a critical area for future investigation.

Several techniques for cooling mass concrete structures were developed in order to increase structural integrity and reduce the influence of cement hydration, which sometimes causes cracking in concrete structures, negatively affecting their durability. This research focuses on cooling system design, initial investment, and the influence of different refrigerants on cooling system performance aims in producing higher quality massive concrete. Cooling aggregates in massive concrete structures such as desert dams can be performed by employing cooled air from an air conditioning duct system or chilled water. The experimental study illustrates the relationship between the coefficient of performance COP, the evaporator temperature, cooling capacity, and refrigerant mass flow rate as a function of the evaporator temperature, cooling capacity, and refrigerant mass flow rate. The findings of the experiments were utilized to verify a numerical model developed utilizing engineering equation solver (EES) software. The performance of the vapor compression of the cooling systems was compared using alternative refrigerants, including R22, R32, and R410a at different operating conditions. This study revealed that R22 refrigerant has a higher coefficient of performance than R32 and R410A, while R32 has the highest cooling capacity among other refrigerants.

To implement the Kigali Amendment to the Montreal Protocol, the global academic community has intensified its research on environmentally friendly refrigerant substitutes. This effort aims to effectively reduce greenhouse gas emissions and facilitate the achievement of carbon neutrality goals. In this study, 14 key influencing factors were identified through the Delphi method, and the Decision-making Trial and Evaluation Laboratory (DEMATEL) approach was innovatively applied to systematically analyze the interrelationships among these factors. The results indicate that technological innovation related to refrigerant substitution ranks first with a centrality score of 5.429, confirming it as the core driving factor for refrigerant substitution. Subsequently, through the integration of Interpretive Structural Modeling (ISM) and Cross-impact Matrix Multiplication Applied to Classification (MICMAC), a hierarchical structure of influencing factors was further developed. This clarified high-driving factors such as government policies and life-cycle costs, as well as highly interrelated factors including climate conditions, greenhouse gas emissions, and performance coefficients. The key contribution of this paper is its success in overcoming the limitations of single-factor analysis by integrating multiple dimensions of influencing factors to construct a hierarchical classification. This innovative and systematic theoretical framework not only offers a scientific basis and decision-making support for refrigerant substitution but also possesses substantial theoretical value and practical guidance. Furthermore, it serves as an essential reference for advancing the development of low-carbon refrigeration technologies.

Heat pumps are widely regarded as a key technology for sustainable heating, offering a pathway to significantly reduce fossil fuel dependency and combat the climate crisis. However, replacing individual gas boilers with heat pumps in multi-unit residential buildings remains a substantial challenge despite its immense potential to lower urban greenhouse gas emissions. To address this, the following paper describes the development of a compact, modular heat pump system designed to replace conventional gas boilers, focusing on the building and testing of a prototype for such a modular heat pump system. The prototype supports multiple functionalities, including space heating, cooling, and domestic hot water production. The performance advantages of two different compressor technologies were exploited to optimize the efficiency of the complete system and the pressure lifts associated with applications for heating and domestic hot water production. Thus, measurements were conducted across a range of operating points, comparing different heat pump module types. In the case of the piston compressor module, the Carnot efficiency was in the range of 47.2% to 50.4%. The total isentropic efficiency for floor heating and domestic hot water production was above 0.45 for both piston and rotary compressors.

Heat pump water heaters (HPWHs) are a proven technology for water heating that has been commercialized. The adoption of HPWHs for domestic and commercial water heating is growing rapidly because of their superior performance compared with alternative water heating methods. Whereas most existing systems use R-134a as a working refrigerant, R290 has gained major attention owing to its superior thermodynamic properties. The goal of the current study is to assess the performance of residential HPWH with R290 as a direct refrigerant replacement for R134a. Two units of a 50 gal HPWH were used in this experimental study. A baseline unit contained R134a refrigerant, and a prototype unit contained R290 refrigerant. The prototype unit was developed through the modification of a commercially available HPWH unit to achieve a low charge of R290 refrigerant. Another major modification was the replacement of the baseline compressor with a compressor designed for R290. Tests were conducted in a field environment (a research and demonstration house) using programmed drawn profiles daily. The prototype that reduced the charge by 43–47% provided displayed performance comparable to the baseline unit regarding first-hour rating (FHR) and the uniform energy factor (UEF).

The global warming potential of many working fluids used nowadays for vapor compression refrigeration systems and heat pumps is very high. Many of such fluids, which are used in currently operating refrigerators and heat pumps, will have to be replaced. In order to avoid a redesign of the system, it would be very helpful if efficient and ecological alternative working fluids for a given plant could be found. With modern process simulation tools such a selection procedure seems possible. However, it remains unclear how detailed such a model of a concrete plant design has to be to obtain a reliable working fluid ranking. A vapor compression heat pump test-rig is used as an example and simulated by thermodynamic models with different levels of complexity to investigate this question. Experimental results for numerous working fluids are compared with models of different complexity. Simple cycle calculations, as often used in the literature, lead to incorrect results regarding the efficiency and are not recommended to find replacement fluids for existing plants. Adding a compressor model improves the simulations significantly and leads to reliable fluid rankings but this is not sufficient to judge the adequacy of the heat exchanger sizes and whether a given cooling or heating task can be fulfilled with a certain fluid. With a model of highest complexity, including an extensive model for the heat exchangers, this question can also be answered.

In HVAC system, the oil circulation is inevitable because the compressor requires the oil for lubrication and sealing. A small portion of the oil circulates with the refrigerant flow through the system components while most of the oil stays or goes back to the compressor. Because oil retention in refrigeration systems can affect system performance and compressor reliability, proper oil management is necessary in order to improve the compressor reliability and increase the overall efficiency of the system. This paper describes a numerical analysis of oil distribution in each component of the commercial air conditioning system including the suction line, discharge line and heat exchanger. In this study, system modeling was conducted for a compressor, discharge line, condenser, expansion valve, evaporator and suction line. Oil separation characteristics of the compressor were taken from the information provided by manufacturer. The working fluid in the system was a mixture of a R-410A refrigerant and PVE oil. When the oil mass fraction (OMF) was assumed, oil mass distribution in each component was obtained under various conditions. The total oil hold-up was also investigated, and the suction line contained the largest oil hold-up per unit length of all components.

Savasta notes that his company's approach - inject dye and scan with a hand-held ultraviolet lamp - not only detects refrigerant but also spots compressor lubricating oil, which generally accompanies a refrigerant leak.

One of the most talked-about issues in the industry's changeover from HCFC to HFC refrigerants is when the per-pound cost of the former is expected to overtake the cost of the latter. There has been a recent, rapid rise in the cost of all refrigerants, primarily due to raw material issues beyond the control of the HVACR industry. One way to hold down the cost of refrigerants is by using as little virgin refrigerant as possible. Maintaining leak-tight systems means having to buy less new refrigerant to replace the stuff that leaked out.